1. Field of the Invention
The present invention relates to a microinstruction controlled data processor for generating the addresses of microinstructions by using the information in the microinstruction which has been previously read out.
2. Description of the Prior Art
As a method for assigning the addresses of microinstructions to be read out, there exists a method by which the addresses are assigned in accordance with the information in the immediately preceding microinstructions. In accordance with this method, a branch-on-condition instruction 2 read out assigns the page addresses of microinstructions 3 and 4 in case such a microinstruction as is shown in FIG. 1 is to be read out. The microinstructions 3 and 4 are simultaneously read out by that page address, and at the same time the displacement address is generated in accordance with the branch condition, which is assigned by the microinstruction 2, so that one of the microinstructions 3 and 4 read out is selected by that displacement address. The shifts from the branch-on-condition instructions 3 and 4 to other microinstructions 5, 6 and 7 are similarly executed. According to the method thus practised, therefore, serial branch-on-condition instructions can also be executed. Since, however, the address written in the microinstruction read out has to be used to read out the subsequent microinstruction, one machine cycle has to be considerably elongated more than the cycle period of a microinstruction memory.